The method MEK inhibitor by Vogelsang et al. [43] was used to determine the

limit of detection (LOD), limit of identification (LOI), and limit of quantification (LOQ). The calibration curve was based on calibration standards (in 1 vol% HNO3) of 0, 5, 10, 25, 50, and 100 μg/L. The curve was linear up to 25 μg/L, and non-linear at higher concentrations (100 μg/L deviated −34% from the extrapolated linear curve). The non-linearity of the curve was accounted for by the instrument using a non-linear fitting curve through zero. The LOD, LOI, and LOQ were calculated based on the calibration points 5, 10, and 25 μg/L (in the linear range) by comparing the calibration signals with signals of spiked samples in each fluid. LOD values of 2.1, 0.5, and 0.5 μg/L Fe were determined in citric acid, in 10 mM NaCl, and in NaCl + BSA, respectively. The corresponding LOI numbers were 4.1, 1.0, and 1.0 μg/L Fe, respectively. The LOQ values were determined to be 6.0, 1.4, and 1.5 μg/L Fe in citric acid, in 10 mM NaCl, and in NaCl + BSA, respectively. The recoveries of 5, 10, and 25 μg/L spiked samples, which should not deviate more than 15% from 100%, were all between 94 and 107%.

Since the acidified selleck chemicals HNO3 and NaOH solutions were similar to the calibration standard matrix, their LOD, LOI, and LOQ values were lower compared with the other solutions, <2.1, <4.1, and <6.0 μg/L Fe, respectively. Solution samples of HNO3, NaOH, citric acid, and NaCl + BSA (two samples after 24 h, all samples after 168 h) were diluted 12.5 times to ensure that concentrations were within the calibration range. The blank values

of all samples were positive and subtracted from the significantly higher solution sample values. The blank values were <1% of the sample values in NaCl, <1.7% in citric acid and HNO3, and 24% after 10 min, 16% after 1 h, and <1.7% after 24 or 168 h in NaCl + BSA. Relatively high blank values (between 1.3 and 22 μg/L Fe) and their variation in the BSA contacting fluids were attributed to the iron content of BSA, as previously reported in Lundin et al. [44]. This influence was accounted for in average values and standard deviations using a background correction for Fe in BSA (see supporting information). Surface compositional analysis was performed using X-ray photoelectron Ketotifen spectroscopy, XPS. Spectra were recorded using a Kratos AXIS UltraDLD X-ray photoelectron spectrometer (Kratos Analytical) using a monochromatic Al X-ray source (150 W) on areas of approximate size 700 μm × 300 μm. Wide spectra (survey scans) were run to identify elements present in the outermost surface oxide (information depth of a few nanometers). High resolution spectra (20 eV pass energy) were acquired for the main bulk compositional elements Cr 2p, Fe 2p, and O 1 s of each test coupon including carbon (C 1 s).